Murray, Jackson's personal doctor, has pleaded not guilty to felony involuntary manslaughter.
The investigation prompted L.A. police to ask the attorney general's office to look into the prescribing practices of seven other doctors.
It was decided Wednesday that those doctors will not face charges. However, one of them was referred to the California Medical Board for prescribing drugs to a Jackson alias.
The state investigation included the search of a prescription drug database that tracks doctors who prescribe controlled substances. The database also monitors the quantity and recipients of those drugs.
The Associated Press contributed to this report.